Evolutionary development of a new generation of extreme RF (x-RF) electronics at frequencies >100 GHz and high power based on known approaches requires a Johnson������������������s figure of merit (JFOM) orders of magnitude superior to that of wide bandgap materials such as GaN. The two main material properties that the JFOM considers are critical breakdown field and drift saturation velocity. Novel ultra-wide bandgap (UWBG) materials with high critical breakdown fields satisfy the first part of the equation. The saturation velocity limit, however, which determines the transit times and frequency limits, cannot be easily overcome. This is due to the nature of bonding in UWBGs, leading to high optical phonon scattering rates and significant related energy losses. It is clear that classical steady-state transport and scaling alone cannot provide for the desired frequency range and targeted power performance. As such, the governing hypotheses of the proposed Center for ultra-wide bandgap extreme-RF electronics (CUXRFE) are: ��������� High fields in UWBG materials allow for transport conditions beyond the classical steady state transport, such as ballistic transport or velocity overshoot of electrons or other quasi-particles, and allow for short transit times unattainable by scaling alone. ��������� In order to exploit intrinsic transient transport phenomena, extrinsic barriers to device performance must be addressed . These include contacts, surfaces, and interfaces required to support high field transport and short transit times.

By integrating wide and ultra-wide bandgap collector regions with AlGaAs/GaAs HBTs, we intend to provide a 10x improvement in power density over current state-of-the-art power HBTs. AlGaAs/GaAs HBTs are well-established with proven high-gain performance throughout the mm-wave regime. This is in large part due to the high quality of the AlGaAs/GaAs emitter-base junction and well-controlled p-type doping in the GaAs base, which yield large emitter injection efficiency and low base resistance, respectively. The breakdown voltage, which determines the output power, is limited by the collector region������������������s critical electric field. We propose to replace the traditional (Al)GaAs collector with an ultra-wide bandgap Al(Ga)N collector in order to significantly boost the power handling of these devices. The proposed heterostructures will be realized via state-of-the-art direct wafer bonding, and will be thoroughly characterized to establish their promise for future high-power, high-frequency devices.

The use of aluminum nitride as a host platform for quantum materials simultaneously addresses the needs for a wide bandgap, well controlled fabrication techniques, ability to combine optics and electronics on a single platform, and the presence of many defect states that can potentially act as qubits. Many AlN point defects have been well-characterized and exhibit spatially localized states far away from the band edge. Our objective for the AlN-based qubit system is to control wanted and unwanted defects in all doping regimes necessary for technical applications. Advances in single-crystal AlN substrate technology with average dislocation densities below 1x103 cm-2 and large areas of wafers dislocation free, developed in the Sitar group, have yielded the capability of obtaining high structural quality and high purity AlN thin films. Obtaining such a low dislocation density allows for direct point defect control instead of extended defects determining the point defect formation. Control over unwanted defects and elimination of extended defects will be essential for the realization of the room temperature qubit.

A thin film sputter deposition system for sub nanometer-controlled deposition of single and multilayer stacks of various dielectric materials is proposed. Targeted to the specific needs of a highly structural and optical quality multilayer deposition crucial for UV optoelectronic applications, the system will guarantee: high lateral and vertical film uniformity across the layer stack, sharp interfaces, high conformity, full process parameter control, and in-situ thickness monitoring. An additional in-line surface characterization by X-ray photoelectron spectroscopy and electron beam deposition of metal layers will enhance the capability of the sputter system to analyze complex semiconductor/metal/dielectric interfaces and prepare contamination free passivation and contact layers for optoelectronic devices. The deposition system is in particular capable to fabricate high reflective UV dielectric Distributed Bragg Reflectors as required for UV microcavity laser and anti-reflecting films for photodiodes and other optoelectronic devices operating in the UV-wavelength range. The deposition system will promote the development of future ultra-low threshold microcavity and polariton laser through the U.S. Army funded project.

We propose the Engineering Research Center for Hybrid Inorganic Photonic Integrated Circuits (HIPICs), which will drive innovation, and engineering of novel photonic systems that expands the applications of PICs into the UV and VIS range of the electromagnetic spectrum by integrating ultrahigh bandgap semiconductors AlGaN with recently emerging high performance photonic materials such hybrid perovskites and semiconducting quantum dots. The resulting developed systems will expand the utilization space of PICs to high-power, high-speed technologies for not only sensing and communications, but will also pave the way for advancements in quantum computing. NC State University is uniquely positioned to host this ERC as it is the leading institution for the development of the ultrahigh bandgap semiconductor technology, and it is also home for closely related centers, such as Power America. In addition NC State University is one of the frontier institutions for research and discovery of organic and hybrid photonic materials and devices.

We propose a basic science program that aims to understand the shallow donor to DX transition and to develop practical strategies to suppress or even eliminate its occurrence in AlN. Although the model material is AlN, the understanding and possible solutions brought forth by this comprehensive program will be generally applicable to other materials.

Novel ultra wide bandgap materials such as AlGaN, ZnO, and GaO are developed for applications in UV optoelectronics, low loss high power devices, and next generations sensing and detection. Because of the wide bandgap of these materials doping is often challenging with available dopants resulting in low carrier concentrations, low mobility, and high compensation. A better understanding of the doping process is only possible if the electrical properties are thoroughly known. A powerful method to determine the electrical properties are Hall measurements. In order to accelerate our research we propose the purchase of a Lake Shore 8400 Series Hall measurement setup. The system includes fully integrated instrumentation, a magnet and power supply, capability to measure over a wide temperature range (15 K to 1,273 K) and AC field measurement capabilities.

This project aims to develop AlGaN-based avalanche photodiode (APD) structures to replace the existing photomultiplier tube (PMT) technology presently used in a vast number of nuclear detectors. The incorporation of these APD structures can result in increased functionality of nuclear detectors employing scintillating materials by vastly reducing the cost, size and high-voltage driver requirements associated with use of PMTs. The greatly reduced geometric footprint of APD detector structures will enable device scaling to include imaging and 3-D stacking capabilities.

Quantum Cascade Lasers (QCLs) utilize transitions between sub-bands in the conduction or valence bands to generate coherent light from infrared down to THz frequencies. Unlike conventional laser diodes (LDs), QCLs are unipolar devices where the emitted light is determined primarily by the device design, i.e., layer thickness and composition, rather than material properties. As such, it is possible to tune the emission of QCLs over a wide range within the same materials system. In addition, since the same electron can emit light several times by tunneling to the next quantum well in the cascade, these devices can have quantum efficiency greater than one and potentially higher output power than conventional LDs. Herein, we propose to develop QCLs using high-aluminum-content AlGaN and AlN layers, which offer a band offset of ~1.8 eV and with that a wide tunability range. The QCL structures will be grown on native AlN substrates offering low dislocation density, growth of uniform AlGaN alloys and interface control on the monolayer scale. These are all necessary technological ingredients that we have demonstrated over the past few years.

The proposed research will extend the applicability of wide bandgap semiconductors beyond the traditional limits imposed by the unipolar (Baliga������������������s) figure of merit (BFOM) by demonstrating a path to superjunction structures based on novel doping and defect control processes. This will lead to a new generation of devices that take advantage of the expected capabilities of III-nitrides but are not limited by doping or implantation technology. Superjunction device structures based on AlGaN are proposed where they exploit the doping selectivity observed in different III-nitride polar domains and the lateral polar patterning technology developed at the WideBandgaps Laboratory at NCSU. In addition, further control of point defects will be realized through the use of Fermi level control schemes based on engineered illumination by the use of UV (blue) lasers surface selective during the growth of the device structure. Such structures will eventually allow for significant breakdown voltages exceeding 5 kV and significant low on-resistance, beyond the expected rated BFOM. This research will provide for a transformative and disruptive technology for power electronics and also provide a breakthrough technology for other applications such as efficient deep UV emitters for water purification. The successful demonstration of such disruptive technology would revolutionize energy switching and transmission, energy storage, and related applications in electrical motor drives and other power intensive applications within the US. As such, the White House has recognized the need to build America������������������s leadership in this technology as part of the manufacturing innovation institutes. In general, this research will directly lead to materials that will be used for applications that deal with the preservation and extension of natural resources by: (1) allowing for the efficient ���������������use and transmission of electrical energy, (2) availability of clean potable water through ���������������disinfection by the use of UV, and (3) the detection of pollutants and other effluents. This ���������������program will provide the opportunity to educate a Ph.D. student with support from an undergraduate student on the growth and characterization of wide bandgap materials while participating with the group������������������s international collaborators network.